Transcript
Gyadari Ramesh, Dr.G.Chandra Mohan Reddy / International Journal Of Engineering
Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp.1975-1995
1975 | P a g e
Analysis of Optimization of Blank Holding Force In Deep
Drawing By Using LS DYNA
Gyadari Ramesh, Dr.G.Chandra Mohan Reddy
Department of Mechanical Engineering, Osmania University, Hyderabad-500085.
ABSTRACT
Sheet metal forming problems are typical
in nature since they involve geometry, boundary
and material non-linearity. Cup drawings involves
many parameters like punch and die radius,
clearance, lubrication, blank holding force and its
trajectories etc. So designing the tools for cup
drawing involves a lot of trial and error
procedure. To reduce number of costly trial error
steps, the process can be simulated by using finite
element packages. Even the finite element package
gives an approximation towards the solution. The
experimentation is inevitable. The aim is to study
analysis of optimization of blank holding force
developed for cup drawing operation by using
explicit finite element package LS DYNA. One of
the basic problems in deep drawing is wrinkling.
Wrinkling can be avoided by using blank holding
force. But higher the blank holding force (BHF),
higher is the frictional force, so more will be
tensile stresses in cup wall there by promote
tearing failure at the punch corner. Hence BHF
needs to optimized so as to prevent the wrinkling
and at the same time to prevent tearing failure. In
this work die design is done for a cup of 30mm
diameter and deep with 1 mm thickness. For the
same blank holding force is calculated from the
empirical formula. The same is simulated on an
explicit finite element package LS DYNA. By an
iterative procedure the optimum blank holding
force is obtained and presented. B H F in deep
drawing is an essential parameter to be
determined optimally to avoid formation of
wrinkles. It is also necessary to at the same time to
determine the force in drawing operation and
failure of the cup. Higher the B H F, higher is the
frictional forces between the blank and blank
holder, so higher the loads required for drawing
operation and higher the strains developed in the
cup walls between the die and punch, thereby
reducing thickness of the section. In this thesis
optimum blank holding force has been found out
by checking the condition of nonformation of
wrinkles at different coefficient of friction at
(0.045, 0.06, 0.1, 0.13, and 0.15) and at different
die radius (2, 3, 4, 5,6mm) and the values of blank
holding force has been taken where no wrinkles
has been formed for different coefficient of
friction and for different die radius and the
graphs are plotted and the results are studied. h-
Method is used for mesh convergence stability of
max vonmises stress is taken as a parameter to
check the convergence.
Keywords – Deep Drawing by Using LS DYNA,
Blank Holding and blank holding force (BHF).
I. INTRODUCTION
Sheet metal forming is one of the most
widely used manufacturing processes for the
fabrication of a wide range of products in many
industries. The reason behind sheet metal forming
gaining a lot of attention in modern technology is due
to the ease with which metal may be formed into
useful shapes by plastic deformation processes in
which the volume and mass of the metal are
conserved and metal is displaced from one location to
another. Deep drawing is one of the extensively used
sheet metal forming processes in the industries to
have mass production of cup shaped components in a
very short time. In deep drawing, a flat blank of sheet
metal is shaped by the action of a punch forcing the
metal into a die cavity Sheet metal forming is one of
the most common manufacturing processes to
plastically deform a material into a desired shape.
Products include hundreds of automotive
components, beverage cans, consumer appliances,
submarine hulls, and air craft frames. Based on the
geometry, the volume and the material, sheet metal
forming can be divided into various categories such
as stamping, deep drawing, stretch forming, rubber
forming, and super plastic forming. Among these,
Stamping and deep drawing are the most common
operations.
Deep drawing products in modern industries
usually have a complicated shape, so these have to
undergo several successive operations to obtain a
final desired shape. Trimming of the flange is one of
those operations and that is used to remove the ears
i.e. to have uniform shape of the flange on all the
sides of the final product. These are formed due to
uneven metal flow in different directions, which is
primarily due to the presence of the planar anisotropy
in the sheet.
The main concern of the deep drawing
industry is to optimize the process parameters in
order to get a complete deep drawn product with least
effects and high limiting drawing ratio. In order to
achieve this optimization objective a large number of
solution runs need to be performed in order to search
for the optimum solution. Furthermore, the quality of
Gyadari Ramesh, Dr.G.Chandra Mohan Reddy / International Journal Of Engineering
Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com
Vol. 3, Issue 4, Jul-Aug 2013, pp.1975-1995
1976 | P a g e
the products can be increased. With reference to an
economical success it is very important to put better
and cheaper products faster on the market than other
competitor‟s. A substantial aid for this is the
numerical simulation. Costs and time for tool
adapting could play an outstanding roll. Furthermore,
changes in design while fabricating a prototype are
usual. By means of numerical simulation, potential
forming problems can be recognized during
fabricating a first tool. Despite many advantages of
the numerical simulation, it must be said, that there
are costs for hardware, software, training and for the
simulation itself. However, it is an effective means
for making forming processes and new products
cheaper. Tool loads can be computed and overloads
can be predicted by means of FEM, which is very
difficult in practical experiments.
The depth of draw may be hallow, moderate
or deep. If the depth of the formed cup is more than
its diameter, the process is called Deep Drawing.
Parts of various geometric and sizes are made by
drawing operation, two extreme example being bottle
caps, automobiles panels etc. the simplest example is
the drawing of a flat bottom cylindrical cup.
In the drawing of a cylindrical cup, a round
sheet metal blank, is placed over a circular die
opening and is held in place with a blank holder. The
punch travels downward and forces the blank into the
die cavity, forming a cup. The important variables in
deep drawing are the properties of sheet metal, the
ratio of blank diameter to punch diameter, the
clearance between the punch and die, the punch
corner radius and die corner radius, the blank holder
force, friction and lubrication. The forces occurring
during drawing are bending at the radii, friction
between blank holder and sheet metal, die and sheet
metal, punch and sheet metal and compression at
flange area or extremity of cup. Usually Drawing is a
process of forming a flat, pre-cut, metal blank into a
hollow shape, either cylindrical or box-shaped, by
pressing it into a die cavity without excessive
wrinkling, thinning, or fracturing. Typical parts
produced by drawing include beverage cans,
containers of all shapes and sizes, and automobile
and aircraft panels. Deep drawing process is
influenced by some parameters like residual stresses,
Blank holding force etc.
Residual stresses also play a very important
role in how a formed part in a deep drawn cup. These
stresses can become so large in a deep drawn cup that
cracks are formed in the cup wall. These residual
stresses can be removed by annealing the cup right
after the deep drawing. However in most cases it is
desire to avoid the annealing process. This process
increases the production costs, and can lead to an
inexpedient production flow and can give problems
with regard to maintaining close tolerances due to
distortion during annealing process.
B H F is an important parameter in deep
drawing process. It is used to suppress the formation
of wrinkles that can appear n the flange of the drawn
part. When increasing the B H F, stress normal to the
thickness increases which restrains any formation of
wrinkles. However, the large value of
the B H F will cause fracture at the cup wall and
punch profile. So, the B H F must be set to a value
that avoids both process limits of wrinkling and
fracture. Avoid wrinkling and tearing such that at ach
punch travel (L), the following relations must be
satisfied:
FBH >F wrinkling and FBH